Since digital signals are advantageous for reducing noise and obtaining high s/n (ratio of signal to noise), digital signals are widely used in various devices. When recording an analog signal, such as a sound signal, on a magnetic tape, it is more advantageous to record a digital signal obtained from the analog signal than to directly record the analog signal for this reason. An analog signal is converted into a digital signal, such as a PCM (pulse code modulation) signal and then the PCM signal is recorded on a magnetic tape. When reproducing, the recorded PCM signal is detected by reproducing heads and then the PCM signal is reconverted into an analog signal.
In such a device, a series of groups of bits (a group of bits is referred to as a word hereinafter) is produced by sampling the magnitude of the analog signal. When recording, a plurality of bits included in one word are simultaneously recorded via a plurality of recording heads on a magnetic tape. Accordingly, when reproducing the digital signal, a plurality of simultaneously recorded bits should be scanned and reproduced by a plurality of reproducing heads simultaneously. If these bits of a word are not simultaneously reproduced, the reconverted analog signal may include noise and be distorted.
The reason distortion and noise occur in the reconstructed analog signal is that there is divergence in the relative position of the reproducing heads and the recorded portions on the magnetic tape. The divergence of the heads is called skew. There are two types of skews which respectively occur because of different reasons. One is called "static skew" while the other is called "dynamic skew". The static skew is usually occurs because of lack of uniformity in the positions and the azimuth of a plurality of head gaps. The dynamic skew usually occurs because of the unstable movement of the magnetic tape. The static skew can be readily corrected by modifying the positions and azimuths of the head gaps. However, the dynamic skew can not be corrected unless the movement of the magnetic tape is perfectly regulated. Perfect control of the movement of a magnetic tape can not be expected and thus dynamic skew is inherent in such an apparatus.
In a conventional type of apparatus, an electrical circuit for compensating for the skew is usually employed. Such an electrical circuit is called a deskew circuit and is usually complex in construction. For instance, a deskew circuit has a plurality of delay circuits corresponding to each track for compensating for the static skew. In another deskew circuit, each bit signal is modulated by given modulation technique, such as phase modulation and frequency modulation, so that each modulated signal can provide a clock signal whereby bit data are recorded and reproduced in synchronization. Although such deskew circuit is workable for compensating for the skew, compensation for drop outs (omission of reproduction) of a plurality of bits is not readily achieved.